Methoxybenzopyrene 4,5-Oxides Labeled with Carbon-13: Electronic Effects in the NIH Shift

Article abstract of DOI:10.1021/jo00350a024

The synthesis of 9-methoxy-4,5-dihydrobenzopyrene-4-13C4,5-oxide and -5-13C4,5-oxide and of 8-methoxy-4,5-dihydrobenzopyrene-4-13C4,5-oxide is reported.The compounds were synthesized in yields of 15percent each from unlabeled precursors. 13C NMR analysis of the conversion of the 4,5-oxides to 4-phenols and 5-phenols (NIH shift) revealed a very strong electronic effect of a 9-methoxy substituent, which gave only the 4-phenol, and a significant but weaker effect of an 8-methoxy substituent, which gave both phenols with the 5-phenol predominating.